Duncan Yo-Yo string pack includes 5 white colored strings for plastic and metal yo-yos. 100% cotton strings are thicker than other cotton strings and thus are preferred by most of the yo-yoers. These Duncan cotton strings can be used with most types of yoyos and are popular among beginners and advanced yo-yo players. People new to yo-yoing prefer complete cotton yo-yo strings to get most friction, allowing them to practice a wide variety of tricks, spins, and looping.